1. Field of the Invention
The present invention relates to a semiconductor device substrate and a semiconductor device fabrication method, particularly to a semiconductor device substrate in which a solder resist is applied onto a predetermined substrate and a semiconductor device fabrication method using the substrate.
2. Description of the Background Art
Demands on semiconductor devices have been recently increased in the field of electronics. A semiconductor device is generally constituted by forming a wiring layer made of a metal, such as copper, on an insulating substrate, such as a glass-epoxy substrate, and mounting of a semiconductor element on the wiring layer. The semiconductor element and the wiring layer are connected to each other by solder or a bonding wire. In this case, so-called solder resist is formed on the substrate in order to prevent a chemical change of the wiring-layer surface and to prevent formation of a solder bridge between adjacent solder junctions.
FIG. 13 is a perspective view of a conventional semiconductor device substrate on which a solder resist is formed. Referring to FIG. 13, a semiconductor device substrate 10 has a plate-shaped substrate 1 and a solder resist 5 formed on the substrate 1. The substrate 1 is almost rectangular and has a major side 1a and a minor side 1b. The substrate 1 is made of the so-called glass-epoxy substrate formed by impregnating glass fiber with epoxy resin and has a superior insulating property. A printed wiring layer (not illustrated) is formed on the surface of the substrate 1. To protect the surface of the printed wiring layer, a solder resist 5 is applied to the surface of the substrate 1. The solder resist 5 is made of, for example, epoxy resin and a hole 5a is formed on the solder resist 5. The hole 5a exposes the printed wiring layer formed on the surface of the substrate 1. Thereby, it is possible to electrically connect the exposed printed wiring layer with a semiconductor device mounted on the layer. Moreover, because the printed wiring layer is covered with the solder resist 5 at other portions, it is possible to prevent the surface of the printed-wiring layer from oxidizing. The solder resist 5 is formed on the surface of the substrate 1 through screen printing.
Problems of the prior art are described below by referring to the accompanying drawings.
FIG. 14 is a perspective view of a substrate shown to explain problems of the prior art. Referring to FIG. 14, the substrate 1 is greatly different from the solder resist 5 in linear expansion coefficient in general. Specifically, the substrate 1 has a smaller linear expansion coefficient because it contains glass fiber. However, the solder resist 5 has a linear expansion coefficient larger than that of the substrate 1 because the solder resist 5 is made of only an organic matter. Therefore, the substrate 1 is warped due to cooling or heating in the cooling process after forming the solder resist 5 or the bonding process for mounting a semiconductor element on the solder resist 5 after formed. Therefore, when housing the semiconductor device substrate 10 in a magazine 50 by mounting the substrate 10 on a rail 30, pushing it with a pusher 40, and conveying it in the direction shown by an arrow 11, the substrate 10 is warped and thereby, it is difficult to automatically convey the substrate 10. As a result, problems occur that the substrate 10 is incorrectly conveyed and fabrication processes are complicated.
Therefore, the present invention is made to solve the above problems and its object is to provide a semiconductor device substrate to be easily conveyed and a semiconductor device fabrication method using the substrate.
A semiconductor device fabrication method according to an aspect of the present invention includes the steps of forming a layer having a linear expansion coefficient A different from that of a semiconductor element mounting, plate-shaped substrate having major and minor sides and containing an organic matter on the substrate, warping the substrate with the layer formed on it along its minor-side direction, and conveying the warped substrate.
According to the above steps, the substrate is not warped along its major-side direction because it is warped along its minor-side direction. As a result, it is possible to decrease the whole warp of the substrate and easily convey the substrate.
It is preferable that the step of warping the substrate in its minor-side direction includes previously adjusting linear expansion coefficients of a substrate so that the difference between the linear expansion coefficient A and the linear expansion coefficient B of the substrate in its minor-side direction becomes relatively large and the difference between the linear expansion coefficient A and the linear expansion coefficient C of the substrate in its major-side direction becomes relatively small. In this case, only by adjusting linear expansion coefficients of the substrate, it is possible to securely warp the substrate along its minor-side direction in the subsequent step.
Moreover, it is more preferable that previously adjusting linear expansion coefficients of a substrate includes adjusting linear expansion coefficients in major- and minor-side directions by arranging a plurality of first fibers extending in the major-side direction of the substrate and a plurality of second fibers extending in the minor-side direction of the substrate in the substrate and adjusting densities of the first and second fibers. In this case, it is possible to easily control linear expansion coefficients in major- and minor-side directions only by adjusting densities of the first and second fibers.
It is still more preferable that the first and second fibers are glass fibers and the substrate contains matrix epoxy resin for covering the glass fibers.
It is still more preferable that the step of warping the substrate in its minor-side direction includes pressing the surface of the substrate so that the substrate is warped along its minor-side direction. In this case, by pressing the surface of the substrate, it is possible to warp the substrate along its minor-side direction through a simple step.
It is still more preferable that the step of warping the substrate along its minor-side direction includes attracting the surface of the substrate so that the substrate is warped in its minor-side direction. In this case, by attracting the surface of the substrate, it is possible to warp the substrate along its minor-side direction through a simple step.
It is still more preferable that the step of warping the substrate along its minor-side direction includes heating the substrate and then cooling the substrate and warping the substrate. In this case, because the substrate is heated, then cooled, and warped, the warped substrate is not easily warped in other directions. As a result, it is possible to securely warp the substrate.
It is still more preferable that a layer contains at least one selected from the group consisting of melamine resin, epoxy resin, acrylic resin, and polyimide resin. In this case, because these resins respectively constitute a solder resist, it is possible to form a solder resist on the substrate.
It is still more preferable that a semiconductor device fabrication method further includes a step of forming a conductive layer on a substrate before forming a layer and a step of forming a layer includes forming the layer so as to expose a part of the surface of the conductive layer. In this case, it is possible to protect the conductive layer by the layer and electrically connect a semiconductor element to the exposed part of the surface of the conductive layer.
It is still more preferable that the step of forming the layer includes forming a layer having a hole reaching the conductive layer on the substrate on which the conductive layer is formed. The semiconductor device fabrication method further includes mounting a semiconductor device on the substrate electrically connected with the conductive layer through the hole. In this case, the semiconductor device is completed by mounting the semiconductor element on the substrate electrically connected to the conductive layer through the hole.
A semiconductor device fabrication method according to another aspect of the present invention includes forming a layer having a linear expansion coefficient almost equal to that of a semiconductor element mounting, plate-shaped substrate containing organic matter, on the substrate and conveying the substrate on which the layer is formed.
According to the above steps, the substrate is not warped even if heating and cooling the substrate because the linear expansion coefficient of the substrate is almost equal to that of the layer formed on the substrate. Therefore, a semiconductor device fabrication method capable of easily conveying a substrate is obtained.
It is preferable that the layer contains polyimide resin. In this case, because the linear expansion coefficient of the polyimide resin can be set in a wide range, it is possible to almost equalize the linear expansion coefficient of the polyimide resin with that of a substrate.
It is more preferable that forming the layer includes forming a layer on a substrate having linear expansion coefficients that have been previously adjusted. The substrate has major and minor sides. Previously adjusting the linear expansion coefficients of the substrate includes arranging a plurality of first fibers extending along a major-side direction and a plurality of second fibers extending along a minor-side direction in the substrate and adjusting linear expansion coefficients of the substrate along the major- and minor-side directions by adjusting densities of the first and second fibers. In this case, by adjusting densities of the first and second fibers, it is reliably possible nearly to equalize the linear expansion coefficients of the substrate and those of the layer.
It is still more preferable that the first and second fibers are glass fibers and the substrate contains matrix epoxy resin for covering the glass fibers.
It is still more preferable that a semiconductor device fabrication method further includes a step of forming a conductive layer on the substrate before forming a layer. The step of forming a layer includes forming the layer so as to expose a part of the surface of the conductive layer. In this case, it is possible to protect the conductive layer by the layer and electrically connect a semiconductor element to the exposed part of the surface of the conductive layer.
It is still more preferable that forming a layer includes forming a layer having a hole reaching the conductive layer on the substrate on which conductive layer is formed. The semiconductor device fabrication method further includes mounting a semiconductor element on the substrate electrically connected to the conductive layer via the hole. In this case, the semiconductor device is completed by mounting the semiconductor device on the element.
A semiconductor device substrate according to the present invention is provided with a plate-shaped substrate having major and minor sides and containing an organic matter and a layer formed on the surface of the substrate and having a linear expansion coefficient A different from that of the substrate. The substrate is warped along its minor-side direction.
Because the semiconductor device substrate thus constituted is warped along its minor-side direction, the substrate is not warped along its major-side direction. As a result, it is possible to easily convey the substrate.
It is still more preferable that the substrate has a minor-side-directional linear expansion coefficient B and a major-side-directional linear expansion coefficient C and the difference between a linear expansion coefficient A and linear expansion coefficient B is relatively large and the difference between the linear expansion coefficient A and linear expansion coefficient C is relatively small. In this case, because the difference between minor-side-directional linear expansion coefficients becomes larger than the difference between major-side-directional linear expansion coefficients, it is possible to securely warp the substrate along its minor-side direction.
It is still more preferable that the substrate includes a plurality of first fibers extending in its major-side direction and a plurality of second fibers extending in its minor-side direction. By adjusting densities of the first and second fibers, major- and minor-side-directional linear expansion coefficients are adjusted. In this case, by adjusting densities of the first and second fibers, it is possible to adjust linear expansion coefficients of the substrate by a simple method.
It is still more preferable that the first and second fibers are glass fibers and the substrate contains matrix epoxy resin for covering the glass fibers.
It is still more preferable that the layer includes at least one of melamine resin, epoxy resin, acrylic resin, and polyimide resin.
It is still more preferable that the semiconductor device substrate is further provided with a conductive layer formed between the substrate and the layer. A hole for the semiconductor element to electrically connect with the conductive layer is formed on the layer.
A semiconductor device substrate according to still another aspect of the present invention is provided with a plate-shaped substrate containing an organic matter and a layer formed on the surface of the substrate and having a linear expansion coefficient almost equal to that of the substrate.
The semiconductor device substrate constituted as described above is not warped because the linear expansion coefficient of the substrate is almost equal to that of the layer formed on the substrate. Therefore, it is easy to convey the substrate.
It is still more preferrable that the layer contains polyimide resin. In this case, because the linear expansion coefficient of the polyimide resin can be set to any value, it is easy to almost equalize linear expansion coefficients of the layer and substrate.
It is still more preferable that the substrate have major and minor sides and include a plurality of first fibers extending along a major-side direction and a plurality of second fibers extending along a minor-side direction. By adjusting densities of the first and second fibers, major-and minor-side directional linear expansion coefficients are adjusted. In this case, by adjusting densities of the first and second fibers, it is possible to equalize linear expansion coefficients of the substrate and the layer.
It is still more preferable that the first and second fibers are glass fibers and the substrate contains matrix epoxy resin for covering the glass fibers.
It is still more preferable that the semiconductor device substrate is provided with a conductive layer formed between the substrate and the layer. A hole for the semiconductor element to electrically connect with the conductive layer is formed on the layer.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.